This revised proposal requests support for the cloning and characterization of the murine mutant gene weaver (wv) and its normal allele. Weaver is an autosomal recessive gene that very selectively disrupts neuronal differentiation and causes cell death in the cerebellum and in the midbrain. Evidence to date points to wv causing deficits in neurite formation in both the dopamine- containing neurons of the midbrain and the granule cells of the cerebellum. These deficits lead to arrested neuronal migration of cerebellar granule cells and their eventual death and to death of a subset of dopamine-containing neurons in the substantia nigra, pars compacta; the mouse homologues of the neurons that die in Parkinson's disease patients. A unique feature of this plan is its pairing of advantages of functional cloning with locational cloning methods. The strategy is designed to identify candidates for wv and its normal allele by isolation of genomic and coding sequences from l) the chromosomal wv region (chromosome 2l in human and l6 in mouse) by YAC technology and 2) brain sources enriched for wv transcripts by a variety of subtractive libraries. The candidates derived from each method will be quickly screened for appropriate chromosomal location using somatic cell hybrids to identify candidates that map to distal chromosome l6. Those passing this screen will be subsequently screened on Southern blots from our linkage assay to identify candidates that map to the wv region. Only these candidate gene(s) will be tested for ability to rescue the defective wv phenotype in an in vitro functional assay. The genes discovered as a result of this research are likely to be part of a cascade necessary for neuronal differentiation as well as part of the system that is altered in Parkinson's disease and hereditary ataxias that involve the dopamine-containing pathways. Certainly, the identification of genes and proteins that maintain the neurons that die in these diseases would open new possibilities for treatment.